Redeye is the appearance of an unnatural reddish coloration of the pupils of a person appearing in an image captured by a camera with flash illumination. Redeye is caused by light from the flash reflecting off blood vessels in the person's retina and returning to the camera.
A large number of image processing techniques have been proposed to detect and correct redeye in color images. In general, these techniques typically are semi-automatic or automatic. Semi-automatic redeye detection techniques rely on human input. For example, in some semi-automatic redeye reduction systems, a user manually identifies to the system the areas of an image containing redeye before the defects are corrected.
Many automatic redeye reduction systems rely on a preliminary face detection step before redeye areas are detected. A common automatic approach involves detecting faces in an image and, subsequently, detecting eyes within each detected face. After the eyes are located, redeye is identified based on shape, coloration, and brightness of image areas corresponding to the detected eye locations. In general, face-detection-based automatic redeye reduction techniques have high computation and memory resource requirements. In addition, most of the face detection algorithms are only able to detect faces that are oriented in an upright frontal view; these approaches cannot detect faces that are rotated in-plane or out-of-plane with respect to the image plane.
U.S. Pat. No. 6,407,777 to DeLuca discloses in-camera detection and correction of redeye pixels in an acquired digital image. U.S. Pat. No. 6,873,743 to Steinberg discloses automated real-time detection and correction of redeye defects optimized for handheld devices. US published patent applications 2005/0047655 and 2005/0047656 to Luo et al. disclose detecting and correcting redeye in a digital image and in embedded systems, respectively.
Automatic red eye detection algorithms can sometimes wrongly identify an image region as red eye artefact. Those regions are called False Positives (FP). Although somewhat rare, applying red eye correction to them can result in a visually displeasing image. It is desired to have a technique that reduces the number of false positives by using face location and/or orientation information.